Variable time constant circuit for use in an electronic musical instrument

ABSTRACT

In the variable time constant circuit of this invention, at least either or both of the resistor and capacitor included in the time constant circuit and acting as the elements for determining the time constant thereof are split into a plurality of units and a normally open or closed switching element selectively closed or opened concurrently with performance of the instrument is connected in parallel with the split resistor or in series with the split capacitor. Such a variable time constant circuit can be triggered by encoded pattern pulses and is used, for example, as an envelope control circuit, a tone coloring circuit, or the oscillating frequency or duration determining circuit portion of a percussion sound oscillator included in each rhythm sound source of the automatic rhythm instrument.

United States Patent [191 Okudaira Jan. 21, 1975 [75] Inventor: Mitsuo Okudaira,Hamamatsu,

Japan [73] Assignee: Nippon Gakki Seizo Kabushiki Kaisha, Hamamatsu-shi, Shizuoka-ken, Japan [22] Filed: June 21, 1973 [21] Appl. No.: 371,997

[30] Foreign Application Priority Data Park 84/1.26 X

3,518,352 6/1970 Plunkett 84/l.03

3,525,796 8/1970 Franssen 84/l.24 X 3,688,010 8/1972 Freeman 84/l.24 X

Primary Examiner-Richard B. Wilkinson Assistant Examiner-U. Weldon Attorney, Agent, or FirmFlynn & Frishauf, P.C.

[57] ABSTRACT In the variable time constant circuit of this invention, at least either or both of the resistor and capacitor included in the time constant circuit and acting as the elements for determining the time constant thereof are split into a plurality of units and a normally open or closed switching element selectively closed or opened concurrently with performance of the instrument is connected in parallel with the split resistor or in series with the split capacitor. Such a variable time constant circuit can be triggered by encoded pattern pulses and is used, for example, as an envelope control circuit, a tone coloring circuit, or the oscillating frequency or duration determining circuit portion of a percussion sound oscillator included in each rhythm sound source of the automatic rhythm instrument.

9 Claims, 21 Drawing Figures :m w 9,5 l

5% 5137 P 34il 29 l l W4 From Selector SW14 'FIG.5A

Pmmammz 1 ms 3,861,263

. SHEET -tUF 6 From Selector SW i4 FIG.I2

I\- 23 A H2 H5 2 294. mlml I From Selector SW i4 VARIABLE TIME CONSTANT CIRCUIT FOR USE IN AN ELECTRONIC MUSICAL INSTRUMENT BACKGROUND OF THE INVENTION This invention relates to a time constant circuit for use in an electronic musical instrument, and more particularly to a variable time constant circuit whose time constant is controlled by a trigger pulse and preferably in synchronism with the playing of the musical instrument.

In electronic musical instruments such as keyboard electronic musical instruments which are designed to play ordinary melody or chord tones consisting of voices of various wind instruments (trumpet, saxophone, clarinet, flute, oboe, etc.) and various stringed instruments (guitar, violin, violoncello, etc.) upon selective operation of a plurality of keys juxtaposed on keyboards, or automatic rhythm instruments which are arranged to automatically play the tones of various percussion instruments (snare drum, bass drum, claves, maracas, cymbals, etc.) upon selective operation of a plurality of buttons, as is well known in the art, a large number of time constant circuits each including one or more resistors and one or more capacitors, or a reactance coil and a capacitor are used.

A keyboard electronic musical instrument in which there is incorporated an automatic rhythm section for playing percussion sounds in addition to an inherent organ section for playing melody and cord tones has heretofore been put to practical use and has also been well known as an automatic rhythm instrument.

Taking such an automatic rhythm instrument as an example of various electronic musical instruments described above, typical time constant circuits are utilized in an envelope control circuit for controlling the envelope of each of various percussion sounds, in a tone coloring filter for controlling the tone color of each envelope-controlled percussion sound, or in an oscillating frequency or duration control circuit portion in each percussion sound oscillator.

As is well known to one skilled in the art the time constant of a time constant circuit can be continuously varied over a wide range using a variable resistor or a variable capacitor.

However, in a time constant circuit for use in such an automatic rhythm instrument it is necessary to vary as quickly as possible the time constant of the time constant circuit to a desired value when the instrument is played. For this reason, time constant circuits utilizing variable resistors or variable capacitors are scarcely used in such an automatic rhythm instrument or another type electronic musical instrument.

Thus, most of the time constant circuits which have been used in electronic musical instruments comprise a plurality of parallel-arranged time constant circuits having fixed time constant which are selected by the player prior to or during performance.

However, time constant circuits constructed as above described have complicated circuit constructions and hence are expensive.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide an improved time constant circuit for use in an electronic musical instrument wherein a single time constant circuit is used which is constructed to permit instantaneous selection of any desired time constant among a plurality of time constants concurrently with the playing of the instrument.

According to this invention, there is provided an electronic musical instrument including a variable time constant circuit comprising a resistor and a capacitor for determining the time constant, at least either of the resistor and capacitor being split into a plurality ol units, and at least one normally open or closed switching element connected in parallel or series with said split resistor or capacitor unit or units concurrently with the operation of the instrument.

According to a preferred embodiment of this invention, such a variable time constant circuit is used as an envelope control circuit and/or a tone coloring filter contained in each rhythm sound source of such an automatic rhythm instrument which utilizes a white noise source.

According to another embodiment of this invention, the variable time constant circuit described above is used as the oscillating frequency or duration control circuit portion of a percussion sound oscillator included in respective rhythm sound sources of another type automatic rhythm instrument in which the percussion sound oscillators of CR oscillation type are substituted for the white noise sources in the former type rhythm sound sources.

According to a further preferred embodiment of this invention, the variable time constant circuit is supplied with and triggered by an encoded pattern pulse.

The automatic rhythm instrument so constructed can produce rhythm sounds having a number the same as, or larger than, those produced by conventional rhythm instruments with a smaller number of rhythm sound sources.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic block diagram of an automatic rhythm instrument in accordance with the invention;

FIG. 2 shows a practical circuit arrangement of each of rhythm sound sources shown in FIG. 1 which utilizes a variable time constant circuit embodying the invention;

FIGS. 3A to 3D show waveforms at various points of the circuit shown in FIG. 2;

FIG. 4 shows a practical circuit arrangement of a modified rhythm sound source embodying the invention;

FIGS. 5A to 5D show waveforms at various points of the circuit shown in FIG. 4;

FIGS. 6 to 9 show different practical circuit arrangements according to further embodiments of this inven' tion;

FIG. 10 shows a practical circuit arrangement of another modification of FIG. 2 (or any one of FIGS. 4 and 6 to 9);

FIGS. 1 I to 14 are practical circuit arrangements embodying another type rhythm sound source shown in FIG. 1; and

FIG. 15 shows a practical circuit arrangement of one modification of FIG. 11 (or of any one of FIGS. 12 to 14).

DESCRIPTION OF THE PREFERRED EMBODIMENTS An automatic rhythm instrument of the invention will now be described with reference to the accompanying drawings, but it should be understood the the invention is never limited to that illustration.

The automatic rhythm instrument illustrated in FIG. 1 comprises a clock pulse generator 11 for generating a repetitive basic tempo pulse train having a frequency corresponding to the shortest beat unit (generally, a quaver or a semiquaver) required to form various sets of rhythm pattern pulses to be described hereinafter; a multistage frequency dividing counter chain 12 which comprises, in this example, four stage flip-flops or binary counters 121, 122, 123 and 124 connected in series; a rhythm pattern pulse encoding matrix 13 constructed to be described later and operative to convert the output pulses received from the binary counters 121 to 124 into various types of rhythm pattern pulse trains such as for waltz, march or rumba; rhythm selector switches 14 selectively operated by a player prior to performance; a plurality of rhythm sound sources S1, S2 Sn, of later described arrangement, such as those of the cymbals, maracas, snare drum and base drum; and a sound reproducing system 15 including a volume control VR, an amplifier A and a loudspeaker P which are arranged in the order mentioned.

As is well known to one skilled in the art, the rhythm pattern pulse encoding matrix 13 is usually constituted by a diode matrix circuit M which is arranged to selectively connect diodes D to the predetermined ones of a plurality of crosspoints at which a plurality of column lines connected to the two output lines of the binary counters 121 to 124 are respectively interconnected with a plurality of row lines which are impressed with clock pulses from the clock pulse generator 11; and AND logic and OR logic circuits each having inputs connected to a predetermined combination of the row lines.

Reference numeral 10 in FIG. 1 denotes a feedback switch provided, if required, to change the rhythm pattern cycle from the four-beat type based on the period in which the clock pulse generator 11 produces 16 clock pulses per cycle to the three-beat type based on the period in which 12 clock pulses are generated thereby per cycle.

Prior to performance on an automatic rhythm instrument, the player operates selectively the selector switches 14 to set one or more of the desired rhythm sound sources S1 to Sn at a condition triggerable by the selected one or more of the various sets of rhythm pattern pulse trains derived out of the rhythm pattern encoding matrix 13. Then, the player manipulates a rhythm start button (not shown) for automatically delivering the desired rhythm sound or sounds from one or more preselected rhythm sound sources, thereby emanating the desired rhythm sound or sounds through the sound reproducing system 15.

Following two constructions are generally used for respective rhythm sound sources S1 to Sn.

The rhythm sound source of one construction comprises a white noise source, an envelope control circuit constructed of an integrating circuit responsive to a rhythm pattern pulse train preselected by the selector switches 14 for controlling the envelope of the white noise signal from the white noise source, and a tone coloring filter for controlling the tone color of the white noise signal whose envelope has been controlled in response to an output signal from the envelope control circuit.

The rhythm sound source of the other construction comprises an externally energized percussion sound oscillator constructed of a CR oscillator which generates a signal having a predetermined frequency, and an envelope control circuit consisting of a CR integrating circuit adapted to be triggered by the rhythm pattern pulse train preselected by the selector switches 14 for generating an envelope control signal utilized to fire or energize the percussion sound oscillator.

In the case of an automatic rhythm instrument utilizing the former type rhythm sound sources, at least either of the resistor and capacitor used in the envelope control circuit and/or tone coloring filter included in the respective rhythm sound sources is split into a plurality of units, and a normally open or closed switching element which is selectively short-circuited or opencircuited in accordance with triggering pulses is connected in parallel with the split resistor unit or units and/or in series with the split capacitor unit or units.

Switching elements suitable for this purpose may comprise field effect transistors with their gates each connected to the desired one of additional output lines L1, L2 Ln diagramatically shown in FIG. I and provided for the selector switches 14 which are selectively operated by the player prior to a rhythm performance, the source-drain paths or conduction channels of respective field effect transistors being connected in parallel with corresponding split resistor units or in series with corresponding split capacitor units. The same purpose can also be accomplished by a mechanical switch including a transfer contact arranged to be opened or closed interlockingly with the operation of the predetermined one of the selector switches 14.

In the case of an automatic rhythm musical instrument utilizing the latter type rhythm sound source, a variable time constant circuit is utilized in which at least either of the resistor and capacitor used in the oscillating frequency or duration control circuit portion of the percussion sound oscillator, and/or the envelope control circuit thereof is split into a plurality of units, and at least one switching element similar to that described above is connected in parallel with the split resistor unit or units in series with the split capacitor unit or units.

FIG. 2 is a practical circuit arrangement of any one of the rhythm sound sources S1 to Sn shown in FIG. 1 which utilizes one form of a variable time constant circuit embodying the invention.

The rhythm sound source is provided with an input terminal 21 adapted to receive a rhythm pattern pulse train preselected by the selector switches 14 shown in FIG. 1. The input terminal 21 is connected via a resistor 22 to the base of a pup grounded-emitter transistor Q1 acting as a C class amplifier 23. The input terminal 21 is also connected to a positive power source terminal 26 via a parallel circuit consisting of a resistor 24 and a capacitor 25. The collector of transistor 01 is connected to a grounded negative power source terminal 28 (hereinafter referred to as the ground) via a resistor 27 and also to an envelope control circuit 29 consisting of a CR integrating circuit in accordance with the invention via a diode D1 of the indicated polarity. The envelope control circuit 29 comprises 21 capacitor 30 with one plate connected to the collector of transistor Q1 via the diode D1 and the other plate grounded; four resistors 31, 32, 33 and 34 connected in series across the capacitor 30 via a switching diode D2 having the same polarity as the diode D1; and two P channel field effect transistors 35 and 36 having their drain-source paths or conduction channels respectively connected in parallel with the corresponding resistors 1 32 and 33 and their gates each connected to the predetermined one of additional output lines L1 to Ln of the selector switches 14, said field effect transistors acting as switching elements.

Further, there is provided a white noise source 41 comprising an npn transistor Q2, acting as a backwardly biased diode, with its emitter connected to the positive power source terminal 26 and its base connected to the ground via a resistor 37; and an amplifier 40 having its input connected to the base or output terminal of transistor Q2 via a capacitor 38 and its output connected to the junction 39 of the resistor 33 with the anode of diode D2. The cathode of diode D2 is connected to the base of an npn grounded-emitter transistor Q3 acting as a C class amplifier 42 and also to the ground via a parallel circuit consisting of the resistor 34 and a capacitor 43. Connected between the collector of transistor Q3 and the positive power source terminal 26 is a parallel resonance circuit, operating at a predetermined frequency and acting as a tone coloring filter 47, which comprises a reactance coil 44, a capacitor 45 and a damping resistor 46 provided if required. The collector of transistor Q3 is also connected to an output terminal 50 via a series circuit including a coupling capacitor 48 and a resistor 49, the output terminal 50 being connected to the sound reproducing system shown in FIG. 1.

The rhythm sound source thus arranged operates as follows:

When a negative rhythm pattern pulse is impressed upon the input terminal 21, transistor Q1 is rendered conductive, causing the diodes D1, D2 to be forwardly biased. Accordingly, the negative input pulse is inverted in phase by the action of transistor Q1 and the resulting positive pulse is charged into the capacitor 30 with a time constant 'm which is determined by the series resistance of the conducting transistor Q1 and diode D1 and the capacitance of capacitor 30. The charged voltage of the capacitor 30 is then discharged with a time constant 'rb which is determined by the capacitance thereof and the resistance of a resistance network comprising four resistors 31, 32, 33 and 34 which are connected in series across the capacitor 30, the two field effect transistors 35 and 36, and the diode D2 to be hereinunder described. The diode D2 is normally maintained at a nonconductive state, but is forwardly biased or becomes conductive when charge-discharge voltages of the capacitor 30 are applied, whereby the diode D2 acts as a switching element.

The envelope of the white noise signal generated by the white noise source 41 is controlled by the chargedischarge voltages of the envelope control circuit 29 described above, and the envelope controlled white noise signal is then applied to the tone coloring filter 47 through the switching diode D2 and the amplifier 42 to be converted into a percussion sound having a desired tone color which can be taken out from output terminal 50.

It is now assumed that the circuit of FIG. 1 is constructed such that negative rhythm pattern pulses P1, P2, P3, P4 each having a value of El volts are impressed upon the input terminal 21 with a timing as shown in FIG. 3A and that negative rhythm pattern pulses P11, P21 and P21, P22 each having a value of E2 volts (E2 B1) are applied to the gates of field effect transistors 35 and 36 with timings as shown in FIGS. 38 and 3C, respectively. With the series resistance of resistors 31 and 34 denoted by R1, the resistance of resistor 32 by R2, and that of resistor 33 by R3, then these resistors are supposed to have a relation R1 2 R2 2 R3. With this construction, the field effect transistors 35 and 36 act as a normally open or nonconductive switching element which is closed or short-circuited only when the negative pulses described above are impressed upon the gates of the respective field effect transistors. As a result, the charging time constant T a of the envelope control circuit 29 is always maintained at a constant value, but the discharging time constant 'rb thereof is varied in the following manner dependent upon the conditions of the field effect transistors 35 and 36.

More particularly, where the first negative pulse Pl (see FIG. 3A), the first negative pulse P11 (see FIG. 3B) and the first negative pulse P21 (see FIG. 3C) are applied simultaneously to the input terminal 21, the gate of field effect transistor 35 and the gate of the field effect transistor 36, respectively, then the discharging time constant of the envelope control circuit 29 has a minimum valve 'rbl, whereas when the second negative pulse P2, the ground potential and the second negative pulse P22 are impressed simultaneously upon the input terminal 21, the gates of the field effect transistor 35 and of the field effect transistor 36, respectively, then the discharging time constant of the envelope control circuit 29 will have a value rb2 which is larger than 'rbl. Furthermore, when the third negative pulse P3, the second negative pulse P12 and the ground potential are applied simultaneously to the input terminal 21, the gates of field effect transistor 35 and of field effect transistor 36, respectively, then the discharging time constant of the envelope control circuit 29 will have a value T173 which is larger than rb2, whereas when the fourth negative pulse P4, and the ground potential are impressed upon the input terminal 21 and the gates of field effect transistors 35 and 36 respectively, then the discharging time constant will have a maximum value 'rb4.

As a result, the envelope of the percussion sound derived from the output terminal of the rhythm sound source is varied in four manners as shown in FIG. 3D under the control of the pulses impressed upon the gates of field effect transistors 35 and 36, producing from a single rhythm sound source any one of four percussion sounds having different envelopes.

FIG. 4 shows a connection diagram of a modified rhythm sound source constructed in accordance with the invention. In the embodiment of FIG. 2, for the purpose of controlling the time constant of the envelope control circuit 29 including a CR integrating circuit, the value of the resistance element in the circuit 29 was varied. In the embodiment of FIG. 4, however, the resistors 32 and 33 and the field effect transistors 35 and 36 shown in FIG. 2 are eliminated, and an envelope control circuit 291 is used wherein in parallel with the capacitor 30 are connected two series circuits respectively consisting of capacitors 61 and 63 and field effect transistors 62 and 64 (normally conducting) which are connected to receive at their gates negative pulses similar to those shown in FIGS. 38 and 3C. This connection is effective to vary the value of capacitance element in the envelope control circuit. With the rhythm sound source utilizing the envelope control circuit 291, when the negative rhythm pattern pulses having timings as shown in FIGS. A to 5C are impressed upon the input terminal 21 and the gates of the field effect transistors 62 and 64, respectively, four types of rhythm sounds having different envelopes can be derived from the output terminal 50 of the rhythm sound source under the control of the pulses impressed upon the gates of the field effect transistors 62 and 64. As shown in FIG. 5D, not only the rising times m1, m2, m3 and m4 (where 'ral m 2 m3 *ra4) but also the decaying times 1'b11, 1'b12, 1'b13 and 'rb14 (where 71711 'rbl2 1b13 rb14) of the produced rhythm sounds are controlled simultaneously, in a manner different from that of the embodiment shown in FIG. 2.

FIG. 6 shows another embodiment of this invention in which the envelope of the percussion sound produced by the rhythm sound source is maintained constant using an envelope control circuit 292 comprising a capacitor 30 and resistors 31 and 34, whereas a tone coloring filter 471 is used which comprises the reactance coil 44, the capacitor 45, the damping resistor 46, and two series circuits connected in parallel with the capacitor 45 and including capacitors 71 and 73 and field effect transistors 72 and 74 arranged to receive at their gates negative rhythm pattern pulses as shown in FIGS. 3B-3C and 5B-5C. With this construction, the tone colors of the percussion sounds derived out of the output terminal 50 are varied in four difference ways under the control of the pulses impressed upon the gates of the field effect transistors 72 and 73 in the same manner as in the previous embodiment.

The modified circuitry shown in FIG. 7 comprises a combination of an envelope control circuit 29 identical to that shown in FIG. 2 and a tone coloring filter 471 identical to that shown in FIG. 6, whereas the circuitry shown in FIG. 8 comprises a combination of an envelope control circuit 291 identical to that shown in FIG. 4 and a tone coloring circuit 471 identical to that shown in FIG. 6. Further modified circuitry of the rhythm sound source shown in FIG. 9 comprises a combination of an envelope control circuit 293 corresponding to the combination of those shown in FIGS. 2 and 4, and a tone coloring filter 471 identical to that shown in FIG. 6.

With the rhythm sound sources shown in FIGS. 7 to 9, it is possible to produce percussion sounds which can be varied over wider ranges than those of the embodiments shown in FIGS. 2, 4 and 6.

Although in the foregoing embodiments field effect transistors were used to act as the switching elements for controlling the time constant of a variable time constant circuit constituting an envelope control circuit and/or a tone coloring filter included in each rhythm sound source of FIG. 1, these transistors may be substituted alternatively, as shown in FIG. 10, with normally open (or closed) mechanical switches W1 and W2 automatically actuated by trigger pulses (conventional relay will do) to attain the same object.

Although in the foregoing embodiments the variable time constant circuits embodying the invention were applied to a rhythm sound source using a white noise source, as will be described hereunder, the novel variable time constant circuit can also be applied to modified rhythm sound sources as shown in FIGS. 11 to 15 wherein a percussion sound generator comprised of a twin-T oscillator (which may be a CR oscillator of any form) is substituted for the white noise source.

FIG. 11 is a practical circuit arrangement ofthis type rhythm sound source embodying the invention.

The rhythm sound source comprises the amplifier 23 constructed as in FIGS. 2, 4 and 6 to 10; an envelope control circuit 294 connected to the collector of the transistor ()1 in the amplifier 23; and a percussion sound generator 81 of a CR oscillation type as hereinunder detailed and adapted to be energized by an out put signal from the envelope control circuit 294. The percussion sound generator 81 includes an npn transistor Q11 having its emitter connected to the ground via three series connected resistors 82, 83 and 84. Connected in parallel respectively with the resistors 82 and 83 are the drain-source paths of P channel field effect transistors 85 and 86, each of whichhas its gate supplied with a negative rhythm pattern pulse train similar to that of FIG. 3B or FIG. 3C. Between the base of transistor Q11 and the ground are connected a twin-T oscillation frequency determining circuit 87. The circuit 87 comprises a circuit 88 consisting of two series connected capacitors 89 and 90 joined parallel with another circuit 91 formed of two series connected resistors 92 and 93, with one junction 94 of said two circuits connected to the base of transistor 011; two resistors 95 and 96 connected in series between the junction of the two capacitors 89 and 90 and the ground; and a eapacitor 97 connected between the junction of the two resistors 92 and 93 and the ground. The collector of transistor Q11 is connected to its base via a resistor 98 and also to the otherjunction 99 of said two circuits 88 and 91 via a feedback capacitor 100.

The collector of transistor Q11 is also connected to the positive power source terminal 26 via a resistor 101 and to an output terminal 501 via a coupling capacitor 102 and a resistor 103.

The envelope control circuit 294 may be a variable time constant type like those shown in FIGS. 2, 4 and 7 to 10, but in this example'consists, like that of FIG. 6, of a fixed time constant type including a resistor 104, the switching diode D2 and a resistor 96 connected in series between the collector of transistor 01 and the ground; and the capacitor 30 connected between the junction of the resistor 104 with the diode D2 and the ground.

The operation of the rhythm sound source so de' signed will now be described.

It should be understood that the percussion sound generator 81 is ordinarily maintained at a deenergizcd state.

When, under this condition, the input terminal 21 is impressed with a negative rhythmpattern pulse train similar to that shown in FIG. 3A or 5A the transistor 01 in the amplifier 23 is rendered conductive.

Accordingly, the capacitor 30 in the envelope control circuit 294 is charged with a positive voltage substantially equal to the positive power source potential with a time constant which is determined by the capacitance of the capacitor 30 and the series resistance of the fired transistor 01 and the resistor 104. The voltage in the capacitor 30 is then discharged through the forwardly biased diode D2 and the resistor 96 with a time constant which is determined by the capacitance of the capacitor 30 and the series resistance of the forwardly biased diode D2 and the resistor 96.

Thus a positive pulse is applied to the gate of by-now dormant transistor Q11, and as a result, the percussion sound generator 81 is momentarily energized by the charge-discharge voltage of the capacitor 30 so as to produce at the output terminal 501 desired percussion sounds having a frequency (in this embodiment chosen to be about 150 hertz) predetermined by the oscillation frequency determining circuit 87 and having a rising and a decaying envelope determined by the chargedischarge voltage of the capacitor 30 in the envelope control circuit 294 acting as an envelope control signal for the produced percussion sounds. In the percussion sound generator 81, the oscillating duration thereof or the sustain time of produced percussion sounds is controlled by a gain in the generator 81. Therefore, if the gates of the field effect transistors 85 and 86 are impressed with rhythm pattern pulse trains similar to those of FIGS. 3B3C or 5B-5C, then the oscillating duration of the percussion sound generator 81 varies in four modes under the control of the pulse trains impressed on the field effect transistors 85 and 86.

FIG. 12 is a connection diagram modified from the embodiment of FIG. 11.

In the modification, a series circuit 111 consisting of a capacitor 112 and a P channel field effect transistor 113 and another series circuit 114 formed of a capacitor 115 and a P channel field effect transistor 116 are connected in parallel with the capacitor 97 in an oscillation frequency determining circuit 87, varing the oscillation frequency of the circuit 87 in four modes under the control of rhythm pattern pulse trains impressed on the gates of field effect transistors 113 and 116.

FIG. 13 shows a connection diagram of another modification of the embodiment of FIG. 12. The modification is designed to vary the value of the resistance element in place of the value of the capacitance element in the oscillation frequency determining circuit 87 of FIG. 11 using two P channel field effect transistors 12a and 12b connected in parallel with two additional resistors 12c and 12d joined in series with the resistors 95 and 96.

FIG. 14 shows a connection diagram of a rhythm sound source comprising a combination of FIGS. 11 and 12.

FIG. 15 shows a connection diagram of a further modification of the embodiment of FIG. 11 using two normally open mechanical switches 13a and 13b (as contacts of relays) in place of the two field effect transistors 85 and 86 in FIG. 11.

The variable time constant circuit according to this invention is applied not only to the above-mentioned musical instrument but also to another type having a substantially identical structure. Namely, in a keyboard electronic musical instrument which produces melody and chord tones each having a predetermined pitch when the keys arranged side by side on the keyboard are selectively depressed, the variable time constant circuit of this invention can be employed as the oscillation frequency control circuit for each of the tone signal generators or as the frequency characteristic determining circuits for each of the tone coloring filters controlling the tone colors of the tone signals from the tone signal generators. This is well known to those skilled in the art.

What is claimed is:

l. A variable time constant circuit for use in rhythm sound sources to vary the rhythm sounds in an electronic musical instrument, and operative on rhythm pulses, comprising:

a pulse source providing rhythm pulses and control pulses in synchronism with the musical sounds of said instrument; and

means for converting said rhythm pulses into rhythm sound signals, including:

at least two different time constant determining circuit elements coupled to each other and coupled in the signal path of said converting means;

one of said time constant determining circuit elements being split into at least two units which are electrically coupled to each other; and

at least one switching element having: a controllable main current conduction path included in one of said split time constant determining circuit element units and being controlled to selectively vary the impedance of said one of said split time constant determining circuit element units to vary the overall time constant of said time constant circuit; and a control electrode coupled to and controlling the impedance of said main current conduction path, said control electrode being impressed with said control pulses produced in synchronism with the musical sounds to vary the conduction path of said at least one switching element, thereby varying said overall time constant and varying said rhythm sounds.

2. A variable time constant circuit as claimed in claim 1 wherein:

' said converting means each comprise a triggerable envelope control circuit including at least one of said time constant determining circuit elements, a white noise source coupled to said at least one time constant determining circuit element and being operative to generate a white noise signal, and a trigger input;

said pulse source is coupled to said envelope control circuits and provides plural sets of encoded rhythm pattern pulse trains, and includes means for selecting at least one of said encoded rhythm pattern pulse trains to trigger said envelope control circuit prior to performance of said rhythm device so as to produce an envelope control signal to control the envelope of the white noise signal from said white noise source;

a tone coloring filter which includes at least one of said time constant determining circuit elements is coupled to the output of said envelope control circuit and is operative to provide a rhythm sound having a predetermined tone color from the envelope controlled white noise signal; and

said time constant determining elements included in said envelope control circuits comprise an integration circuit including at least one capacitor and a plurality of series connected resistors joined across said capacitor; and said at least one switching ele ment is connected with its main current conduction path in parallel with at least one of said series con nected resistors, the impedance of said conduction path being varied in accordance with the selected encoded rhythm pattern pulses, thereby changing the total value of resistance coupled across said capacitor.

3. A variable time constant circuit as claimed in claim 1 wherein:

said converting means each comprise a triggerable duction paths in parallel with at least one of said series connected resistors, and in series with at least one of said parallel connected capacitors. the

envelope control circuit including at least one of pacitors joined across said series connected resistors; and at least two of said switching elements are connected with their respective main current conimpedances of said conduction paths being varied said time constant determining circuit elements, a 5 in accordance with the selected encoded rhythm white noize source coupled to lsaid at leacslttpne time pattern pulse: tllq'ierebylchanging the total value of constant etermining circuit e ement an eing opresistance an t e tota va ue of capacitance. erative to generate a white noise signal, and a trig- 5. A variable time constant circuit as claimed in ger input; claim 1 wherein said converting means each include: said pulse source is coupled to said envelope control a tone coloring filter which includes at least one of circuits and provides plural sets of encoded rhythm said time constant determining circuit elements; pattern pulse trains, and includes means for selecta white noise source operative to generate a white ing at least one of said encoded rhythm pattern noise signal; pulse trains to trigger said envelope control circuit a triggerable envelope control circuit, which includes prior to performance of said rhythm device so as to at least one of said time constant determining cirproduce an envelope control signal to control the cuit elements, coupled to said white noise source; envelope of the white noise signal from said white said pulse source being coupled to said envelope connoise solurce; f h h l d l f trol circuitls and providjjng pllural sets of rhythm tone co oring iter w ic me u es at east one 0 pattern pu se trains, an inc uding means for sesaid time constant determining circuit elements is lecting at least one of said rhythm pattern pulse coupled to the output of said envelope control cirtrains to trigger said envelope control circuit prior cuit and is operative to provide a rhythm sound to performance of said rhythm device so as to prohaving a predetermined tone color from the enveduce an envelope control signal to control the enlope controlled white noise signal; and velope of the white noise signal from said white said time constant determining elements included in noise source; and

said envelope control circuits comprise an integrasaid tone coloring filter being coupled to said envetion circuit including at least one resistor and a plulope control circuit to receive said envelope conrality of parallel connected capacitors joined trolled white noise signal and being operative to across said resistor; and said at least one switching provide a rhythm sound having a predetermined element is connected with its main current conduc- 3O tone color from the envelope controlled white tion path in series with at least one of said parallel noise signal, said tone coloring filter comprising a connected capacitors, the impedance of said conresonance circuit including a reactance coil and a dulctioi:j path being tyartiled in accordalnce with the plurality of parallel connected capacitors joined se ecte encoded r yt in pattern pu ses, t ereby across said reactance coil; and at least one addichanging the total relative value of capacitive imtional switching element having a main conduction pedance coupled across said resistor. path connected in series with at least one of said 4. A variable time constant circuit as claimed in parallel connected capacitors, the impedance of clairrzil wherein: b said conduction path of said additional switching sai converting means each comprise a triggera le element being varied in accordance with the se' envelope control circuit including at least one of 40 lected rhythm pattern pulses, thereby changing the said time constant determining circuit elements, a total relative value of capacitance impedance in white noise source coupledto said at least one time said resonance circuit and varying the tone color. constant determining circuit element and being op- 6. A variable time constant circuit as claimed in erative to generate a white noise signal, and a trigclaim 1 wherein said converting means each include: gciiar iilput; l d d l I a fpercussiondsound generatorhavigg oscillation sai pu se source is coup e to sai enve ope contro requency etermining circuit an w ich includes circuits and provides plural sets of encoded rhythm at least one of said time constant determining cirpattern pulse trains, and includes means for selectcuit elements; ing at least one of said encoded rhythm pattern a white noise source operative to generate a white pulse trains to trigger said envelope control circuit noise signal; prior to performance of said rhythm device so as to a triggerable envelope circuit, which includes at least produce an envelope controlsignal to control the 'one of said time constant determining circuit eleenvelope of the white noise signal from said white ments, coupled to said white noise source; noise solurce; H h h l d l f said pulse source lzieing co pled tlo salid envelfop; conatone co oring iter w 10 inc u es at east one o tro circuits an provi ing p ura sets 0 r ythm said time constant determining circuit elements is pattern pulse trains, and including means for secoupled to the output of said envelope control cirlecting at least one of said rhythm pattern pulse cuit and is operative to provide a rhythm sound trains to trigger said envelope control circuit prior having a predetermined tone color from the enveto performance of said rhythm device so as to prolope controlled white noise signal; and duce an envelope control signal to control the ensaid time constant determining elements included in velope of the white noise signal from said white said envelope control circuits comprise an integranoise source; and tion circuit including a plurality ofseries connected said percussion sound generator being coupled to resistors and a plurality of parallel connected ca- 5 said envelope control circuit to receive said envelope controlled white noise signal and being operative to generate percussion sounds having a predetermined frequency from the envelope controlled white noise signal, said percussion sound generator comprising an amplifier and said oscillation frequency determining circuit which receives said envelope controlled white noise signal, said oscillavelope controlled white noise signal, said oscillation frequency determining circuit including an RC lel with at least one of said series connected resistors, the impedance of said conduction path of said additional switching element being varied in accordance with the selected rhythm pattern pulses.

tion frequency determining circuit including an RC thereby changing the total value of resistance in circuit including at least one resistor and a plurality said RC circuit and varying the percussive sound. of parallel connected capacitors selectively cou- 8. A variable time constant circuit as claimed in pled thereto for resonating at predetermined freclaim 1 wherein said converting means each include: quencies; and at least one additional switching elea percussion sound generator having an oscillating ment having a main conduction path connected in duration control circuit and which includes at least series with at least one of said parallel connected one of said time constant determining circuit elecapacitors, the impedance of said conduction path ments; of said additional switching element being varied in a white noise source operative to generate a white accordance with the selected rhythm pattern noise signal; pulses, thereby changing the total value of capaci- 15 a triggerable envelope control circuit, which includes tance in said RC circuit and varying the percussive at least one of said time constant determining cirsound. cuit elements, coupled to said white noise source; 7. A variable time constant circuit as claimed in said pulse source being coupled to said envelope eonclaim 1 wherein said converting means each include: trol circuits and providing plural sets of rhythm a percussion sound generator having an oscillation pattern pulse trains, and including means for sefrequency determining circuit and which includes lecting at least one of said rhythm pattern pulse at least one of said time constant determining cirtrains to trigger said envelope control circuit prior cuit elements; to performance of said rhythm device so as to proa white noise source operative to generate a white duce an envelope control signal to control the ennoise signal; velope of the white noise signal from said white a triggerable envelope control circuit which includes noise signal source; and

at least one of said time constant determining cirsaid percussion sound generator including an amplicuit elements, coupled to said white noise source; fier having at least one transistor, an oscillation fresaid pulse source being coupled to said envelope conquency determining circuit and said oscillating dutrol circuits and providing plural sets of rhythm ration control circuit and being coupled to said enpattern pulse trains, and including means for sevelope control circuit to receive said envelope conlecting at least one of said rhythm pattern pulse trolled white noise signal and being operative to trains to trigger said envelope control circuit prior generate percussion sounds having a predeterto performance of said rhythm device so as to promined frequency and duration from the envelope duce an envelope control signal to control the encontrolled white noise signal, said oscillating dura velope of the white noise signal from said white tion control circuit comprising a plurality of resisnoise source; and tors connected in series between the emitter of said said percussion sound generator being coupled to amplifier transistor and ground; and at least one said envelope control circuit to receive said enveadditional switching element having a main conlope controlled white noise signal and being operaduction path connected in parallel with at least one tive to generate percussion sounds having a predeof said series connected resistors, the impedance of termined frequency from the envelope controlled said conduction path of said additional switching white noise signal, said percussion sound generator element being varied in accordance with the secomprising an amplifier and said oscillation frelected encoded rhythm pattern pulses, thereby quency determining circuit which receive said enchanging the total value of resistance in said oscillating duration control circuit. 9. A variable time constant circuit claimed in circuit including at least one capacitor and a plurality of series connected resistors selectively coupled claim 1 wherein said switching element comprises a field effect transistor whose drain-source path comthereto for resonating at predetermined frequenprises said main current conduction path and whose cies; and at least one additional switching element gate electrode comprises said control electrode. having a main conduction path connected in paral- UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION PATENT NO. 3, DATED INVENTOR(S) I January 21 1975 Mitsuo OKUDAIRA It is certified that error appears in the ab0veidentified patent and that said Letters Pateni are hereby carrectec' as shown below:

Column 12, line 51 after "a triggerable envelope" insert -control;

Signal and Scaled this twenty-second Day Of July 1975 [SEAL] Arrest:

RUTH C. MASON C MARSHALLDANN Alrtsling Offic Commixsione'r of Patents and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF .CORRECTION PATENT NO. 3,861,263

DATED INVENTOR(S) I January 21 1975 Mitsuo OKUDAIRA It is certified that error appears in the ab0veidentified patent and that said Letters Pareni are hereby corrected as shown below:

Column 12, line 51 after "a triggerable envelope" insert -control--;

Signed and Scaled this twenty-second D21) Of July 1975 [SEAL] A ttesr:

RUTH C. MASON r C. MARSHALL DANN Arresting Officer Commissioner of Parents and Trademark: 

1. A variable time constant circuit for use in rhythm sound sources to vary the rhythm sounds in an electronic musical instrument, and operative on rhythm pulses, comprising: a pulse source providing rhythm pulses and control pulses in synchronism with the musical sounds of said instrument; and means for converting said rhythm pulses into rhythm sound signals, including: at least two different time constant determining circuit elements coupled to each other and coupled in the signal path of said converting means; one of said time constant determining circuit elements being split into at least two units which are electrically coupled to each other; and at least one switching element having: a controllable main current conduction path included in one of said split time constant determining circuit element units and being controlled to selectively vary the impedance of said one of said split time constant determining circuit element units to vary the overall time constant of said time constant circuit; and a control electrode coupled to and controlling the impedance of said main current conduction path, said control electrode being impressed with said control pulses produced in synchronism with the musical sounds to vary the conduction path of said at least one switching element, thereby varying said overall time constant and varying said rhythm sounds.
 2. A variable time constant circuit as claimed in claim 1 wherein: said converting means each comprise a triggerable envelope control circuit including at least one of said time constant determining circuit elements, a white noise source coupled to said at least one time constant determining circuit element and being operative to generate a white noise signal, and a trigger input; said pulse source is coupled to said envelope control circuits and provides plural sets of encoded rhythm pattern pulse trains, and includes means for selecting at least one of said encoded rhythm pattern pulse trains to trigger said envelope control circuit prior to performance of said rhythm device so as to produce an envelope control signal to control the envelope of the white noise signal from said white noise source; a tone coloring filter which includes at least one of said time constant determining circuit elements is coupled to the output of said envelope control circuit and is operative to provide a rhythm sound having a predetermined tone color from the envelope controlled white noise signal; and said time constant determining elements included in said envelope control circuits comprise an integration circuit including at least one capacitor and a plurality of series connected resistors joined across said capacitor; and said at least one switching element is connected with its main current conduction path in parallel with at least one of said series connected resistors, the impedance of said conduction path being varied in accordance with the selected encoded rhythm pattern pulses, thereby changing the total value of resistance coupled across said capacitor.
 3. A variable time constant circuit as claimed in claim 1 wherein: said converting means each comprise a triggerable envelope control circuit including at least one of said time constant determining circuit elements, a white noise source coupled to said at least one time constant determining circuit element and being operative to generate a white noise signal, and a trigger input; said pulse source is coupled to said envelope control circuits and provides plural sets of encoded rhythm pattern pulse trains, and includes means for selecting at least one of said encoded rhythm pattern pulsE trains to trigger said envelope control circuit prior to performance of said rhythm device so as to produce an envelope control signal to control the envelope of the white noise signal from said white noise source; a tone coloring filter which includes at least one of said time constant determining circuit elements is coupled to the output of said envelope control circuit and is operative to provide a rhythm sound having a predetermined tone color from the envelope controlled white noise signal; and said time constant determining elements included in said envelope control circuits comprise an integration circuit including at least one resistor and a plurality of parallel connected capacitors joined across said resistor; and said at least one switching element is connected with its main current conduction path in series with at least one of said parallel connected capacitors, the impedance of said conduction path being varied in accordance with the selected encoded rhythm pattern pulses, thereby changing the total relative value of capacitive impedance coupled across said resistor.
 4. A variable time constant circuit as claimed in claim 1 wherein: said converting means each comprise a triggerable envelope control circuit including at least one of said time constant determining circuit elements, a white noise source coupled to said at least one time constant determining circuit element and being operative to generate a white noise signal, and a trigger input; said pulse source is coupled to said envelope control circuits and provides plural sets of encoded rhythm pattern pulse trains, and includes means for selecting at least one of said encoded rhythm pattern pulse trains to trigger said envelope control circuit prior to performance of said rhythm device so as to produce an envelope control signal to control the envelope of the white noise signal from said white noise source; a tone coloring filter which includes at least one of said time constant determining circuit elements is coupled to the output of said envelope control circuit and is operative to provide a rhythm sound having a predetermined tone color from the envelope controlled white noise signal; and said time constant determining elements included in said envelope control circuits comprise an integration circuit including a plurality of series connected resistors and a plurality of parallel connected capacitors joined across said series connected resistors; and at least two of said switching elements are connected with their respective main current conduction paths in parallel with at least one of said series connected resistors, and in series with at least one of said parallel connected capacitors, the impedances of said conduction paths being varied in accordance with the selected encoded rhythm pattern pulses, thereby changing the total value of resistance and the total value of capacitance.
 5. A variable time constant circuit as claimed in claim 1 wherein said converting means each include: a tone coloring filter which includes at least one of said time constant determining circuit elements; a white noise source operative to generate a white noise signal; a triggerable envelope control circuit, which includes at least one of said time constant determining circuit elements, coupled to said white noise source; said pulse source being coupled to said envelope control circuits and providing plural sets of rhythm pattern pulse trains, and including means for selecting at least one of said rhythm pattern pulse trains to trigger said envelope control circuit prior to performance of said rhythm device so as to produce an envelope control signal to control the envelope of the white noise signal from said white noise source; and said tone coloring filter being coupled to said envelope control circuit to receive said envelope controlled white noise signal and being operative to provide a rhythm sound having a predetermined tone color from the envelope cOntrolled white noise signal, said tone coloring filter comprising a resonance circuit including a reactance coil and a plurality of parallel connected capacitors joined across said reactance coil; and at least one additional switching element having a main conduction path connected in series with at least one of said parallel connected capacitors, the impedance of said conduction path of said additional switching element being varied in accordance with the selected rhythm pattern pulses, thereby changing the total relative value of capacitance impedance in said resonance circuit and varying the tone color.
 6. A variable time constant circuit as claimed in claim 1 wherein said converting means each include: a percussion sound generator having an oscillation frequency determining circuit and which includes at least one of said time constant determining circuit elements; a white noise source operative to generate a white noise signal; a triggerable envelope circuit, which includes at least one of said time constant determining circuit elements, coupled to said white noise source; said pulse source being coupled to said envelope control circuits and providing plural sets of rhythm pattern pulse trains, and including means for selecting at least one of said rhythm pattern pulse trains to trigger said envelope control circuit prior to performance of said rhythm device so as to produce an envelope control signal to control the envelope of the white noise signal from said white noise source; and said percussion sound generator being coupled to said envelope control circuit to receive said envelope controlled white noise signal and being operative to generate percussion sounds having a predetermined frequency from the envelope controlled white noise signal, said percussion sound generator comprising an amplifier and said oscillation frequency determining circuit which receives said envelope controlled white noise signal, said oscillation frequency determining circuit including an RC circuit including at least one resistor and a plurality of parallel connected capacitors selectively coupled thereto for resonating at predetermined frequencies; and at least one additional switching element having a main conduction path connected in series with at least one of said parallel connected capacitors, the impedance of said conduction path of said additional switching element being varied in accordance with the selected rhythm pattern pulses, thereby changing the total value of capacitance in said RC circuit and varying the percussive sound.
 7. A variable time constant circuit as claimed in claim 1 wherein said converting means each include: a percussion sound generator having an oscillation frequency determining circuit and which includes at least one of said time constant determining circuit elements; a white noise source operative to generate a white noise signal; a triggerable envelope control circuit which includes at least one of said time constant determining circuit elements, coupled to said white noise source; said pulse source being coupled to said envelope control circuits and providing plural sets of rhythm pattern pulse trains, and including means for selecting at least one of said rhythm pattern pulse trains to trigger said envelope control circuit prior to performance of said rhythm device so as to produce an envelope control signal to control the envelope of the white noise signal from said white noise source; and said percussion sound generator being coupled to said envelope control circuit to receive said envelope controlled white noise signal and being operative to generate percussion sounds having a predetermined frequency from the envelope controlled white noise signal, said percussion sound generator comprising an amplifier and said oscillation frequency determining circuit which receive said envelope controlled white noise signal, said oscillation frequency determining circuit including an RC circuit inCluding at least one capacitor and a plurality of series connected resistors selectively coupled thereto for resonating at predetermined frequencies; and at least one additional switching element having a main conduction path connected in parallel with at least one of said series connected resistors, the impedance of said conduction path of said additional switching element being varied in accordance with the selected rhythm pattern pulses, thereby changing the total value of resistance in said RC circuit and varying the percussive sound.
 8. A variable time constant circuit as claimed in claim 1 wherein said converting means each include: a percussion sound generator having an oscillating duration control circuit and which includes at least one of said time constant determining circuit elements; a white noise source operative to generate a white noise signal; a triggerable envelope control circuit, which includes at least one of said time constant determining circuit elements, coupled to said white noise source; said pulse source being coupled to said envelope control circuits and providing plural sets of rhythm pattern pulse trains, and including means for selecting at least one of said rhythm pattern pulse trains to trigger said envelope control circuit prior to performance of said rhythm device so as to produce an envelope control signal to control the envelope of the white noise signal from said white noise signal source; and said percussion sound generator including an amplifier having at least one transistor, an oscillation frequency determining circuit and said oscillating duration control circuit and being coupled to said envelope control circuit to receive said envelope controlled white noise signal and being operative to generate percussion sounds having a predetermined frequency and duration from the envelope controlled white noise signal, said oscillating duration control circuit comprising a plurality of resistors connected in series between the emitter of said amplifier transistor and ground; and at least one additional switching element having a main conduction path connected in parallel with at least one of said series connected resistors, the impedance of said conduction path of said additional switching element being varied in accordance with the selected encoded rhythm pattern pulses, thereby changing the total value of resistance in said oscillating duration control circuit.
 9. A variable time constant circuit as claimed in claim 1 wherein said switching element comprises a field effect transistor whose drain-source path comprises said main current conduction path and whose gate electrode comprises said control electrode. 